Intensive radiosonde observations of the diurnal tide and planetary waves in the lower atmosphere over Yichang (111°18' E, 30°42' N), China
Abstract. The characteristics of diurnal tide and planetary waves (PWs) in the troposphere and lower stratosphere (TLS) over Yichang (111°18' E, 30°42' N) were studied by using the data from intensive radiosonde observations in August 2006 (summer month) and January 2007 (winter month) on an eight-times-daily basis. The radiosonde observations of the diurnal tide and PWs in the TLS in the mid-latitudes have seldom been reported. We find that there exists dominant diurnal oscillations in the TLS over Yichang. The observed diurnal tide consists of significant nonmigrating components, which may be owning to the local latent heat release. Since the nonmigrating tides are usually composed of high order modes with smaller vertical wavelengths, which are prone to dissipation in comparison with the low order modes, the observational tidal amplitudes decrease sharply at several heights. Some evident discrepancies between the observations and the GSWM-02 are found, which may result mainly from the inaccurate prediction of the nonmigrating tidal components by the GSWM-02. And, due to the evident seasonal differences of the water vapor mixing ratio disturbance and the tropospheric jet induced turbulence in winter, the diurnal tides in the summer and winter months have some different characteristics. Besides the diurnal tide, obvious quasi 7-day PW (QSDPW) and quasi 10-day PW (QTDPW) are also recognized from our observations in both the summer and winter months. The QSDPWs in the troposphere in both the summer and winter months show a standing wave structure, while the QTDPWs generally exhibit traveling wave characteristics. Spectral analyses reveal that some waves with periods around that of the diurnal tide are generated due to the interactions of the diurnal tide and PWs and the tidal amplitudes are modulated by the PWs, indicating the extensive coupling between the diurnal tide and PWs. Moreover, our observations manifest that the PWs can exert great impacts on the tropospheric jet in winter and the tropopause in both the summer and winter months.